It has been previously proposed to apply a coating to a rock surface in a mine in order to provide support or a gas barrier by spraying an aqueous emulsion of an organic polymer and causing the emulsion to coagulate to produce a flexible coating in the form of a film or skin on the surface.
Polymers which have been disclosed for this purpose include polyurethanes and polychloroprene. The latter has been described in South African Patent No 8203384.
More recently there has been described in WO 98/58886 a composition comprising two parts. One is an aqueous emulsion of an organic polymer such as the copolymer of ethylene and vinyl acetate. The other part is a cementitious composition capable of absorbing at least its own weight of water. The cementitious composition described is an ettringite-forming composition. A well known method of forming ettringite is from calcium sulphate, a source of lime and high alumina cement. In WO 98/58886 high alumina cement is used and the lime is provided by ordinary Portland cement and the calcium sulphate by anhydrite.
In use the two parts are sprayed onto a rock surface of a mine to form a coating. This patent also discloses a dry mixture of solids formed from the cementitious composition and a dried polymer emulsion to which mixture water is subsequently added.
Japanese Patent Application No 05 170496A describes a waterproof resilient floor paving material comprising high alumina cement and per 100 parts by weight of the cement, 5 to 50 parts of fibre, 30 to 300 parts of polymer and 50 to 300 parts of aggregate. The polymer is added to the cement as an aqueous dispersion. The patent reports that when less than 50 parts of aggregate or less than 5 parts of fibre are used sufficient strength is not developed.